In general, thermoplastic resin is widely used to electricity, electronic parts, office machines, car parts and the like due to its relatively good properties such as impact resistance, mechanical strength, moldability, gloss and the like.
As a representative thermoplastic resin, Acrylonitrile-Butadiene-Styrene (ABS) resin is an impact reinforcing agent, and comprises a conjugated diene-based rubber latex, which is a representative polybutadiene having excellent rubber characteristics, as a main ingredient.
The conjugated diene-based rubber latex can be prepared by emulsion polymerization. The emulsion polymerization has advantages that it is easy to modify recipe according to quality level preferentially required and it can prepare various product families when extruding a product produced in the powder form and then mixing thereof with various matrix resins (PSAN, PC, PBT, PVC and the like) and additives (flame retardant, weather resistant stabilizer, antistatic agent, antibiotic and the like).
Meanwhile, particle diameter of the conjugated diene-based rubber latex is closely related to reaction time of the emulsion polymerization. For example, now, the emulsion polymerization reaction should be conducted for 30 hours or longer to prepare large-sized rubber latex having large particle diameter. Thus, there is a disadvantage that the conventional method for preparing the large-sized rubber latex has low productivity.
In order to improve these problems, methods of adding a small amount of additives such as an emulsifier and a vinyl cyanide monomer before starting polymerization or continuously adding the emulsifier are suggested. However, there is a problem that reaction time reduction effect is inadequate. If increasing polymerization reaction temperature to increase reaction speed, rather particle diameter of the rubber latex is reduced and reaction coagulation is increased, and also it causes another problem that reaction pressure is increased by excess reaction heat thereby safety is low during mass production process.
Moreover, when preparing the thermoplastic resin, in the case of mixing the large-sized rubber latex and the small-sized rubber latex prepared by the conventional method, the thermoplastic resin having relatively high low-temperature impact strength and relatively high surface gloss at the same time can be prepared, but there are disadvantages of longer processing time, complex processing process and high cost because the method comprises a process of preparing the large-sized rubber latex and the small-sized rubber latex, respectively, and then mixing thereof.
Accordingly, development of a method for preparing diene-based rubber latex whose particle diameter size is controlled in a short reaction time is urgent.